GEO POLYMER CONCRETE

INTRODUCTION
1.1 General: The basic and most important constructional material for infrastructural development is ordinary portland cement-OPC. Ordinary portland cement(OPC) is conventionally used as the Primary binder to produce concrete. The environmental issues associated with the OPC are Well known. The amount of the carbon dioxide released during the manufacture of OPC due to The calcination of the limestone and combustion of fossil fuel is in the order of one ton for every Ton of OPC produced. In addition, the extent of energy required to produce OPC is only next To steel and aluminium . India is third largest cement producing country in the world, next only to china and japan Despite OPC being highly valuable and wonderful building material, it suffers from variety of Maladies. The maladies include depletion of natural resources like lime stone in production Of OPC, large amounts of energy consumption in manufacture results in global warming and Climate change, cause panic in the whole world, spiraling cost of OPC in developing countries Like India . research has been in progress all over the world accruing several benefits replacement Of OPC with CCMS(Complimentary Cementing materials) like Rice husk ash, silica fume , flyash And others has negated the ill effects of OPC to a large extent. Further the availability of fly ash Worldwide creates opportunity to utilize this by-products of burning coal, as a substitute for OPC To manufacture concrete. CONT-

when used as a partial replacement of OPC , in the presence of water and in ambient Temperature , fly ash reacts with the calcium hydroxide during the hydration process of OPC to Form the calcium silicate hydrate (C-S-H) gel. The development and application of high volume Fly ash concrete, which enabled the replacement of OPC up to 60% by mass is a significant Development.

In 1978, Davidovits proposed that binders could be prepared by a polymeric reaction Of alkaline liquids with the silicon and the aluminium in sources materials of geological origin or By-products materials such as fly ash and these binders are known as geo-polymers . The main Binders produced is a C-S-H gel, as the result of the hydration process.

1.2 Low-calcium Fly-Ash based Geo-ploymer Concrete: Reacting alumino silicate minerals with highly alkaline solution forms geopolymers. concrete manufactured with such geo-polymers is known as GEOPOLYMER CONCRETE. The alumino silicate minerals to be used are class-F fly ash and alkaline Solutions to be used are sodium hydroxide solution, sodium silicate solution. In this Work, low-calcium fly ash-based geo-ploymer is used as the binder, instead ofPortland Or other hydraulic paste, to produce concrete. The fly ash based geo-polymer paste Binds the loose coarse aggregates, fine aggregates and other un-reacted materials Together to form the geo-polymer concrete, with or without the presence of admixtures. The manufacture of geo-polymer concrete is carried out using the usual concrete Technology methods. As in the case of OPC concrete, the aggregate occupy about 75-80% by Mass, in geo-polymer concrete. The silicon and the aluminium is the low-calcium flyash react with an alkaline liquid that is a combination of sodium silicate and sodiumhydroxide solution to form the geo-polymer paste that binds the aggregates and other un-reacted materials.

1.3Fly ash:
According to the American Concrete Institute(ACI) Committee 116R, fly is defined as „the finely divided residue that results from the combustion of ground or powdered coal and that Is transported by flue gasses from the combusyion zone to the particle removal system‟. Fly ash Is removed from the combustion gases by the dust collection system, either mechanically or by Using electrostatic precipitators, before they are discharged to the atmosphere. Fly ash paticles Are typically spherical, finer than portland cement and lime, rangling in diameter from less than 1µm to more than 150µm. The types and relative amounts of incombustible matter in the coal determine the chemical Composition of fly ash. The chemical composition is mainly composed of the oxides of silicon(SiO2), Aluminium (Al2O3), iron(Fe2O3), and calcium(CaO), whereas magnesium. potassium, sodium, titanium, and sulphur are also present in a lesser amount.

1.4 Geo-polymers:
Davidovits proposed that an alkaline liquid could be used to react with the silicon(si) and the aluminium (al) in a source material of geological origin or in byproduct materials such as fly ash and rice husk ash to produce binders. Because the chemical reaction that takes place in this case is a polymerization process. Geo-Polymers are members of the family of inorganic polymers. The chemical composition of the geo-polymer material is similar to natural zeolitic materials, but The microstructure is amorphous instead of crystalline. The polymerization process invoves a subStantially fast chemical reaction under alkaline condition on si-al minerals, that results in a three Dimensional polymeric chain and ring structure consisting of si-o-al-o bonds, as follows.

Mn[-(SiO2)z-AlO2]n.wH2O
Where: M=the alkaline element or cation such as potassium, sodium or calcium; the symbol – indicates the presence of a bond, n is the degree of polycondensation or polymerization; z is 1,2,3, or higher, up to 32.

CONSTITUENTS OF GEOPOLYMERS
2.1Source materials:
Any material that contains mostly silicon(si) and Aluminium (al) in amorphous form is a possible source material for the manufacture of geo-polymer. Metakaolin or calcined kaolin, low-calcium ASTM class F fly ash, natural Al-Si minerals, combination of calculated mineral and non-calcined Materials , combination of fly ash and metakaolin, and combination of granulated blast furnace Slag and metakaolin can be taken as source materials.

low-calcium(ASTM class F) fly ash is preferred as a source material than highcalcium(ASTM class F) fly ah. The presence of calcium in high amount may interfere with the polymerisation process and alter the microstructure. Fly ash is considered to be advantageous due to its high Reactivity that comes from its finer particle size than slag. Moreover, lowcalcium fly ash is more Desirable than slag for geo-polymer feedstock material.

2.2Alkaline liquids :
The most common alkaline liquid used in geo-polymerisation is combination of sodium hydroxide (NaOH) or potassium hydroxide(KOH) and sodium silicate or potassium silicate. The type of alkaline liquid plays an important role in the polymerization process. Reactions Occur at a high rate when the alkaline liquid contains soluble silicates, either sodium or potassium Silicate, compared to the use of the only alkaline hydroxides. That the addition of sodium silicate Solution to the sodium hydroxide solution as the alkaline liquid enhanced the reaction between the source material and the solution. Among the geo-polymerisation of sixteen natural Al-Si minerals, NaOH solution causes a higher extent of dissolution of minerals than the KOH solution.

MANUFACTURING PROCESS
3.1 Material Preparation:
Aggregates used in the manufacture the fly ash-based geo-polymer concrete were in a saturated-surface-dry (SSD) condition. The aggregate selection and proportion were in accordance with the current practice used in making OPC concrete. The alkaline liquid consisted of a combination of sodium silicate solution and sodium hydroxide solution. The sodium silicate solution was purchased from a local supplier. The sodium hydroxide solution was prepared by dissolving the solids, purchased from a local supplier in flakes or pellets form, in water. Both the solutions were premixed the day before use. The alkaline liquid was mixed with the super plasticiser, if any, and the extra-added water, if any, to prepare the liquid component of the geo-polymer concrete mixture.

3.2 Mixing, Placing, and Compaction:

The liquid component of the mixture was then added to the solids particles, and mixing continued for The aggregate and the fly ash were mixed dry in a pan mixer for about three minutes another four minutes in most cases. The fresh fly ash-based geo-polymer concrete could be handled up to at least two hours without any sign of setting and degradation in compressive strength. The fresh geo-polymer concrete could be placed, compacted, and finished in moulds in that time. In all these operations, the equipment and the facilities currently used for OPC concrete were used. For cylinder specimens of 100x200 mm, the mixture was cast in three layers. Eachlayer received 60 manual strokes, and vibrated for 10 seconds on a vibrating table. Insome cases, the common internal needle vibrator was also utilised to successfully compact the fly ashbased geo-polymer concrete.

PAN MIXER

DRY MATERILAS

ADDITION OF LIQUID COMPONENT

FRESH GEOPOLYMER CONCRETE READY FOR PLACING

COMPACTION INTO MOULDS

3.3 Curing:
After casting, the test specimens were covered by a vacuum bagging film. Curing at an elevated temperature was achieved either in the dry curing environment in an oven, or in the steam curing chamber, for a specified period of time. After curing, the concrete specimens were allowed to cool down in the moulds. After releasing from the moulds, the test specimens were left to air dry in ambient conditions in the laboratory until the day of testing.

The cost of one ton of fly ash is only a small fraction, if not free in some parts of the world, of the cost of one ton of Portland cement. In Australia, based on the current bulk cost of sodium silicate solution and sodium hydroxide solids, we have estimated that the cost of chemicals needed to react one ton of fly ash is approximately AU $50. This is significantly smaller than the current price of Portland cement. Therefore, low-calcium fly ash-based geo-polymer concrete is cheaper than Portland cement concrete.

In addition, we have learnt that the appropriate usage of one ton of fly ash earns one carboncredit that currently has a redemption value of about 20 Euros. Based on the data given in this Report, one ton low-calcium fly ash can be utilised to manufacture approximately 2.5 cubic metres of good quality fly ash-based geo-polymer concrete, and hence earn monetary benefits through carbon-credit trade.

Furthermore, the very little drying shrinkage, the low creep, the excellent resistance to sulfate attack, and the good acid resistance offered by the low-calcium fly ash-based geopolymer concrete provides additional economic benefits when used in infrastructure applications.

CONCLUSION
• The reduce of CO2 emissions of geo-polymer concrete makes them a good alternative to Ordinary portland cement. • Produces a substance that is comparable to or better than traditional cements with respect To most properties. • Geo-polymer concrete has excellent properties with in both acid and salt environments.

• Low-calcium fly ash based geo-polymer concrete has excellent compressive strength and is Suitable for structural applications. • Low-calcium fly ash based geo-polymer concrete offers several economical benefits over Ordinary concrete since the cost of fly ash only fraction of cement . More over the bulk cost of Sodium silicate and sodium hydroxide solids are smaller than the current price of portland Cement.

REFERENCES
• Research report on Development and properties of low-calcium fly ash-based geo-polymer concrete by D.Hardjito and B.V.Rangan. • IS 456-2000 indian standard plane and reinforced concrete code of practices, bureau of indian Standards, New Delhi. • Fly ash and its applications as a building material, a booklet published by Govt. of india, National Buildings Organization and UN regional housing center ECAFE, nirman bhavan , New delhi. • Malhotra. V.M. “High performance HVFA concrete. A solution to the infrastructural needs of india” , the indian concrete journal, feb 2002,pp.103-107. • Indian standard mix design procedures for plane and reinforced concrete code of practice, IS 10232: 1982, bureau of indian standards, new delhi. • Shetty.M.S.,‟concrete technology‟ Dhanapat rai publications, new delhi, 2002.